| Modification Notes |
Hemoglobin (Hgb) is coupled to four iron-binding, methene-linked tetrapyrrole rings (heme). The å (16p13.3; 5'-Ω-pseudoz-pseudo å2-pseudo å1-å2-å1-œ1-3') and ∫ (11p15.5) globin loci determine the basic hemoglobin structure. The globin portion of hemoglobin consists of two å chains and two ∫ chains arranged in pairs forming a tetramer. Each of the four globin chains covalently associates with a heme group. The bonds between å and ∫ chains are weaker than between similar globin chains, thereby forming a cleavage plane that is important for oxygen binding and release. High affinity for oxygen occurs upon relaxation of the å1-∫2 cleavage plane. When the two å1-∫2 interfaces are closely bound, hemoglobin has a low affinity for oxygen. Hb A, which contains two å chains plus two ∫ chains, comprises 97% of total circulating hemoglobin. The remaining 3% of total circulating hemoglobin is comprised of Hb A-2, which consists of two å chains plus two ∂ chains, and fetal hemoglobin (Hb F), which consists of two å chains together with two © chains. |